1. Field of the Invention
The present invention relates generally to an alarm. More specifically, the present invention relates to a microprocessor controlled alarm having a unique spatial sound pattern to reduce the noise to persons having to be in close proximity to the alarm, such as an operator of a machine on which the alarm is mounted.
2. Background Art
Alarms are used on mobile machinery and vehicles to warn persons of the danger they may present. Such machinery is used in construction, mining, industrial, and warehouse applications, for instance. Some alarms are sounded only when the vehicle is backed up. An operator of such machinery, such as a fork lift, back hoe, crawler, etc., is subject to the noise of the alarm. Conventional alarms have no particular protection for the operator from intense sound. As a consequence, alarms are often disabled by operators so as to alleviate themselves of the discomfort caused by the noise.
Present day alarms require variable amplifiers and different control circuits for different applications. So, an alarm to be placed on a fork lift used inside a low-ceiled building would be quite different from an alarm placed on a bulldozer used only out in the open in a landfill.
A variable volume horn system for vehicles was disclosed in U.S. Pat. No. 3,173,136 by Atkinson. The horn of Atkinson automatically adjusts its signal level based on the ambient noise. The adjustability is effected using a variable output amplifier.
Munson, et al., (U.S. Pat. No. 3,934,085) also disclose a variable volume horn system. This invention also includes a sensor to determine the volume of the horn signal, and a logic unit to adjust the volume whenever the volume drops below a predetermined level.
A more recent invention for a horn used on moving vehicles is that of Gailbreath, et al., in U.S. Pat. No. 4,603,317. This invention, again, adjusts its signal level based on the ambient noise level. The alarm of the Gailbreath, et al., patent has selectable sound patterns to make the alarm distinguishable from surrounding noise.
In the above patents, no novel housing, or acoustic lens, shapes for the audio transducer are specified. Most such systems utilize a highly directional, truncated horn or similar for the housing; or their goal is a sound pattern that is essentially the same in all directions.
Another issue, not addressed in the prior art, is that of supply voltage. When the alarm supply voltage varies, the usual result is a varying alarm signal, even to the point of being unsatisfactory or failure of the alarm.
Still another facet of the prior art is the shape of the diaphragm and arrangement used in the transducer of an alarm system. The prior art is profuse with dome shaped diaphragms for loudspeakers. For high-fidelity applications, a voice coil is utilized that is not fused to the edge of the dome and the edges of the dome are couched in a well-damped surround to reduce distortion. There is a dearth of prior art alarm systems showing transducer assemblies having good environmental sealing and heat transfer, with the additional benefit of low cost. Current alarm designs have high cost associated with high output levels in almost direct proportion. High fidelity is not an important attribute for an alarm system of the present application.
There is a need, therefore, for a reliable alarm system using a microprocessor to provide functionality such as variable signal level based on the ambient noise, accommodation of varying source voltage, and a plurality of alarm signal types, so the alarm is detectable among background noises. There is also a need for a mobile vehicle alarm system providing a strong alarm signal to the areas most in danger of the vehicle, such as behind the vehicle when it is being backed up, while protecting the operator of the vehicle from high signal strength that might cause hearing damage. An additional need is for a transducer design combining the attributes of good environmental sealing, good heat transfer and low cost, creating a high integrity design housing, allowing the alarm to meet the SAE and ANSI, etc. standard specifications and tests.